.clearfix::after {
  content: '';
  display: block;
  clear: both;
}

header .list {
  width: 100%;
  height: 50px;
  background-color: #fff;
  margin-bottom: 1rem; 
  border-bottom: 1px solid #ddd; 
}

header .list .list-item {
  position: relative;
  float: left;
  margin-left: 20px;
  padding: 0 10px;
  line-height: 50px;
  cursor: pointer;
}

header .list .list-item .tips {
  display: none;
  position: absolute;
  left: 15px;
  bottom: -35px;
  width: 150px;
  height: 30px;
  text-align: center;
  line-height: 30px;
  font-size: 12px;
  background-color: #fff;
  border-radius: 8px;
}
header .list .list-item .tips::before {
  content: '';
  display: block;
  position: absolute;
  top: -10px;
  left: 10px;
  width: 0;
  height: 0;
  border: 5px solid transparent;
  border-bottom-color: #ddd;
}
header .list .list-item .underline {
  position: absolute;
  width: 0;
  height: 2px;
  left: 0;
  bottom: 0px;
  background-color: #f00;
}
header .list .list-item .changeBtn label:hover {
  cursor: pointer;
}
header .list .list-item:hover .underline {
  width: 100%;
  transition: 0.45s;
}
header .list .list-item:hover .tips {
  display: block;
  transition: all 0.5s linear;
  background-color: #ddd;
}

footer {
  margin: 0 auto;
  width: 1200px;
  padding: 1rem 0;
  text-align: center; 
}

footer div {
  margin: 3px;
  font-size: 13px;
  color:#000;
}

footer div a {
  color: #000;
}